Welcome

I think this song is about Christina's career (up until that point). I'm going to explain my meaning lyric for lyric.

"Welcome to the greatest show Greatest show on earth You've never seen before Hear the fairytale unfold"

This is at the beginning of Christina's career. She wants us to watch her from the very beginning.

"What's behind the smoke and glass? Painted faces, everybody wears a mask Are you selling them your soul? Will you be left out in the cold"

I think this is how, at the beginning, peopple take control of her career and make her into something she's not.

"Is it all blue skies Fun and games until you fall? Then you're left without anyone at all"

This is how at the beginning of her career everything was great, but then her popularity started to decline and people began turning on her (fans, the general public).

"You're riding on a shooting star With a smile upon your face But soon the shine fades And you're left out all alone Wondering where did they all go"

Again, everything is going great in her career. She's at the peak of her popularity. She's a shining star. But soon people start turning on her (fans and general public) and she wonders why they are doing it.

"Been jaded, hated Who'll be around when the limelight's faded? Been shut down, pushed down Made to smile when I wanted to frown"

Even though she's being bashed everywhere and by everyone, the people around her want her to appear happy, even though on the inside she's feeling terrible.

"Always taking a bow Always walking the crowd Always making the rounds Always playing the clown"

This explains how everyone was making her do the things she didn't want to do, and in the end it made her a clown.

"Who'll be sticking it out? Who'll be staying around When the lights go down?"

I think this is just her asking who is still going to be successful after their burst of popularity is over.

I hope that makes sense. I'm horrible at explaining stuff lol. It made more sense in my mind...